1. Field of the Invention
The present invention relates to a process for catalytic hydrocarbon recombination, and more particularly to a process for catalytic hydrocarbon recombination for preparing high quality gasoline and diesel fuel.
2. Description of the Related Art
Catalytic cracking, heavy oil catalytic cracking technology is the key technology of oil refining. Catalytic cracking includes wax oil catalytic cracking, heavy oil catalytic cracking; the oils produced by this process are called catalytic hydrocarbons. When processed, normally through a fractionator, the resulting catalytic hydrocarbons may produce dry gas, gasoline, diesel fuel, heavy oil, etc., where gasoline and diesel fuel is up to 70% of the market gasoline and diesel fuel share.
As environmental protection requirements getting increasingly stringent, the standards of the gasoline and diesel fuel become higher and higher. The existing fractionation process for catalytic hydrocarbon has the following deficiency: First, the quality of the gasoline and diesel fuel produced by the existing process is to be improved; the olefin content of the gasoline is too high, octane number is too low, the cetane number of the diesel fuel is too low, and it can not meet the stabilization requirement; Secondly, the existing process is not available for producing various grade of gasoline at the same time, the grade of the products is too narrow; third, the ratio of the gasoline and diesel fuel produced does not match the market requirement, insufficient for the demand of diesel fuel but over sufficient for the demand of gasoline.
The main factor which impacts the quality of the gasoline is the olefin content and the octane number of the gasoline. Recently, the methods taken by oil refining plants to increase the octane number are: 1. Increase high octane number gasoline regulating fraction, such as recombined resulting oil, alkylate, etherized resulting oil, isomerized resulting oil, etc.; 2. Use new catalysts; 3. Adjust the operating condition of catalytic cracking; 4. Adjusting the fractionation rang of gasoline.
The following issues are found from the above methods: 1. High capital cost, high operation cost, capacity limited by the feedstock, and unreasonable use of resource, for example, since recombined resulting oil is the main feed for the polyester, it maximizes the shortage of the polyester feed when large amount of recombined resulting oil is used as high octane gasoline blending fraction; 2. Use of new catalysts could increase the octane number, but it will lead to higher olefin content of the gasoline and decrease the diesel fuel and gasoline ratio; 3. Measures to adjust the operating condition of catalytic cracking and to increase the octane number could also lead to higher olefin content in the gasoline and lower the diesel fuel and gasoline ratio; 4. Measures to adjust the fractionation rang and to get higher octane number will also lead to higher olefin content in the gasoline, even if the adjusting margin is limited. All the methods used to get higher octane number by increasing the olefin content of the gasoline have conflict with execution of new gasoline standard.
The solvent used in the solvent extracting tower to extract the aromatic hydrocarbon composition and non-aromatic hydrocarbon composition is recycled, and it is intersoluble with water. When having recycled in the equipments for a long time, part of the solvent inevitably produces acidic material due to oxidization. Anti-acid is added to remove the acidic material. In the above process, trace olefin can be carried in the feed. In addition, mechanical contaminants can also be generated in the equipments and piping. The color of the recycle solvent will get darker and darker, and high polymer and acidic material accumulate continuously, it will impact the operation of the above process little by little, in the case of serious, it will impact the quality and yield of the product. Therefore, the recycle solvent must be regenerated.
The current solvent regeneration methods include atmosphere or vacuum stripping regeneration, atmosphere or vacuum distillation regeneration, adsorption regeneration and filtration regeneration. The stripping regeneration capacity is low due to the limitation of the stripping gas rate; the operation of the distillation regeneration is too complicated, large amount of solvent is lost, the energy consumption is high, and severe coking is found at the reboiler of the regenerator. Ion exchange resin is commonly used for adsorption regeneration, such as the sulfolane extracting system recycle water regeneration proposed by U.S. Pat. No. 4,919,816. This method can remove the acidic material of the recycle water, minimize the corrosion of the equipment, but can not remove the contaminant of the solvent system. Moreover, alkali solution is required. Chinese patent CN1062007C disclosed a regeneration method of aromatic extraction solvent. This regeneration approach is achieved by adding recycle water to the system, then by filtration and adsorption de-colure. It's disadvantages are as follows: first, the water amount in the system is limited, so it will limit the process capacity; secondly, after the water is added, the contaminant of the solvent can not be isolated before going into the adsorption bed, so fouling frequently happens at the adsorption bed; third, the adsorption bed fail when up to a certain extent due to the limitation of the adsorption capacity of the adsorption bed, so replacement or regeneration of the sorbent is required; fourth, acid and alkali treatment is required for resin regeneration, the operation is complex and it leads to higher cost.